machine oil is probably "smoother and lighter" feeling, but I am OLD school, a tapered seat ball bearing is going to get grease. I have some very Light grade "moly" grease that I use for roller bearing in cold weather, same stuff I use on my bicycles...another application where you are supplying the power and do not want to add any more drag than you have to. also I will grease all of the "Pointy set screw" type bearings on the foot board with the same stuff.